Implement content addressability for plugins

Move plugins to shared distribution stack with images.

Create immutable plugin config that matches schema2 requirements.

Ensure data being pushed is same as pulled/created.

Store distribution artifacts in a blobstore.

Run init layer setup for every plugin start.

Fix breakouts from unsafe file accesses.

Add support for `docker plugin install --alias`

Uses normalized references for default names to avoid collisions when using default hosts/tags.

Some refactoring of the plugin manager to support the change, like removing the singleton manager and adding manager config struct.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
Signed-off-by: Derek McGowan <derek@mcgstyle.net>

docs/reference/commandline/plugin_create.md

@@ -16,9 +16,9 @@ keywords: "plugin, create"
 # plugin create
 
 ```markdown
-Usage:  docker plugin create [OPTIONS] PLUGIN[:tag] PATH-TO-ROOTFS(rootfs + config.json)
+Usage:  docker plugin create [OPTIONS] PLUGIN PLUGIN-DATA-DIR
 
-Create a plugin from a rootfs and configuration
+Create a plugin from a rootfs and configuration. Plugin data directory must contain config.json and rootfs directory.
 
 Options:
       --compress   Compress the context using gzip 

docs/reference/commandline/plugin_inspect.md

@@ -36,8 +36,7 @@ $ docker plugin inspect tiborvass/no-remove:latest
 ```JSON
 {
   "Id": "8c74c978c434745c3ade82f1bc0acf38d04990eaf494fa507c16d9f1daa99c21",
-  "Name": "tiborvass/no-remove",
-  "Tag": "latest",
+  "Name": "tiborvass/no-remove:latest",
   "Enabled": true,
   "Config": {
     "Mounts": [

docs/reference/commandline/plugin_install.md

@@ -21,6 +21,7 @@ Usage:  docker plugin install [OPTIONS] PLUGIN [KEY=VALUE...]
 Install a plugin
 
 Options:
+      --alias string            Local name for plugin
       --disable                 Do not enable the plugin on install
       --grant-all-permissions   Grant all permissions necessary to run the plugin
       --help                    Print usage